Hello there, .
Let me share some information to help you access your QuickBooks account.
Keychain Access is a macOS app that stores your passwords and account information. Since you're using a new mac device, you'd received the same prompt especially if you have stored your QuickBooks username and password in Keychain.
On the other hand, you can refer to these articles to learn more information about accessing your QuickBooks Online:
Keep in touch with us here if you have other questions or concerns. I'm always here to help.